There are known in the prior art ship's tanks, wherein pipes together with other devices such as ladders, control cables for electrical pumps which are located at the lower end section of the discharge pipes, etc., are attached to the inner wall of a tubular casing extending vertically and centrally in the tank, the end sections of which casing are permanently connected to the upper section and the lower section of the tank, respectively, and whose weight is supported by these tank sections.
Those objects which are provided in the casing are attached to it by suitable means at points located between its upper and lower ends, and the casing is arranged to support these completely. The pipes are substantially designed to resist the tangential stresses which are caused by any pressure differential which may exist between the outside and the inside of the pipes, with the result that the pipe material is not exposed to optimum stresses.
Since the ends of the casing are secured in the tank, variations in the temperature of the casing and the tank will came a variation in the force exerted between the casing and the tank due to the resulting, uneven thermal expansion.
Since the casing has to encompass all the pipes, etc., and therefore has a large diameter, and the casing wall is substantially unperforated, considerable transverse forces and bending moments will be exerted on the casing due to the forces which are exerted by the liquid which flows alternately between the starboard and port sides or back and forward in the tank, if the ship is rolling or pitching in the water and the tank is not completely full. These transverse forces are in turn transferred to the tank together with related stress moments.
In addition to the fact that this makes the casing heavy and expensive, the tank also has to have an increased thickness in order to be able to support the weight of the casing and withstand the extra forces resulting from the effects of the temperature differences and the ship's movements.